Inflatable packaging cushions, or airbags, have become well known for cushioning packages and products during shipment. Some airbags are positioned inside a package to provide cushioning of a product within the package and to fill voids between the product and the walls of the package. These are generally smaller airbags, but may in some instances be of considerable size.
Dunnage bags are large volume airbags used to fill voids and secure packages in shipping spaces, such as in trucks, railroad cars, aircraft and shipping containers. Dunnage bags are often positioned between adjacent pallets each containing multiple product packages, and between such pallets and the walls of the shipping spaces.
Airbags may encounter changes in ambient pressure during shipment, the most pronounced effect being due to changes in altitude. For instance, freight aircraft are generally pressurized to the normalized atmospheric pressure at 7500 feet, and trucks and railroad cars may encounter altitude changes of 5000 or more feet in transit routes from sea level across mountains.
At the higher altitudes, there is a decrease in the ambient pressure exerted on the exterior of the airbags, and the increased differential between the external ambient pressure and inflation pressure of the airbags that was set at a lower altitude causes the airbags to expand.
In the case of small volume, well supported airbags acting on sturdy packaging and products, this is generally not a problem, but particular packaging and products may require careful and accurate adjustment of inflation pressure. However, larger volume airbags and particularly dunnage bags have a correspondingly larger increase in dimension which can damage adjacent packaging or the products therein. If the airbag is inside a package, it can expand and deform the package from the inside. In the case of dunnage bags, the expanded dunnage bags can compress and deform the packaging of adjacent products by pushing the package walls inwardly.
A particular example of this problem is in the shipment of flat screen televisions. The packaging carton is designed to surround and protect the perimeter of the flat screen televisions, and to support the flat screen televisions on that perimeter packaging. However, there is no cushioning between the screen of the flat screen television and the outside carton, which therefore consists of a large unsupported panel of cardboard spaced from the screen. This avoids contact between the packaging and the screen, which thereby also avoids possible scratching or pressure damage to the screen. However, when multiple cartons of flat screen televisions are placed on pallets and loaded into shipping containers and the pallets are spaced and secured by inflated dunnage bags, the dunnage bags are in contact with the outside panels of some of the cartons. If the dunnage bags expand too greatly in transit, the panels of the cartons are crushed inwardly. Although actual damage to the flat screen televisions may be avoided because of the spacing provided by the cartons, the flat screen televisions are no longer saleable as an A-stock product and have to be sold as B-stock or “open box” product at a reduced prices and substantial loss of profit. In a worse case example, the flat screen television is actually damaged and cannot be sold at all.
A desired inflation pressure based on the highest anticipated altitude change during shipment of the product can be calculated. In the case of a dunnage bag being used in the shipment of products that will encounter a 5000 foot increase in altitude change, the desired inflation pressure may be on the order of 0.06 PSI, and initial inflation pressure of 0.8-1.0 PSI or above may cause considerable damage when the shipment reaches its highest altitude. It is very difficult for a worker to estimate the correct inflation pressure based on the appearance and feel of the dunnage bag as the dunnage bag is being inflated, and it is also very difficult to measure and adjust the inflation pressure during inflation with currently available equipment and methods.
Accordingly, it would be a substantial advance in the art if the inflation pressure of airbags, and particularly dunnage bags, could be accurately and efficiently established at the time of inflation.